The invention relates to a seat belt retractor provided with an emergency locking mechanism for constraining an occupant by preventing a webbing from being drawn out in a crash of a vehicle or on other occasions, and also provided with an energy absorption mechanism for absorbing an impact load acting between the occupant and the webbing, so as to protect the occupant.
A seat belt retractor which, in a non-use condition, takes up a webbing of a seat belt apparatus attached to a vehicle body or the like and for holding an occupant in the seat is generally provided with inertia sensing means for, in a crash of a vehicle, a rapid acceleration or deceleration of the vehicle body, or the like, detecting this, and also provided with an emergency locking mechanism for, in response to the detection, preventing the webbing from rewinding, so that an occupant can be safely constrained in the seat by the webbing in an emergency such as a crash of a vehicle.
In the case where the emergency locking mechanism operates in a crash of a vehicle, a rapid deceleration of the vehicle body, or the like, if the webbing is perfectly set in a locked condition, a large impact load acts between an occupant and the webbing. Conventionally, therefore, the following seat belt retractor is already practically used. The seat belt retractor is provided with an energy absorption mechanism which, in the case where an impact load acting on the webbing exceeds a definite value, absorbs the impact load while the webbing is drawn out at a certain degree.
As a seat belt retractor provided with such an energy absorption mechanism, known is a seat belt retractor having a configuration in which a torsion bar made of soft steel or the like is interposed between a spool for taking up a webbing and an emergency locking mechanism for blocking the rotation of the spool. Specifically, in a seat belt retractor provided with such a kind of energy absorption mechanism, an emergency locking mechanism adopts a configuration provided with a ratchet wheel which rotates together with the spool, and a pawl which locks the spool via the ratchet wheel with meshing with the ratchet wheel in response to the detection of a crash of a vehicle or the like by inertia sensing means. In addition, a torsion bar is interposed between the ratchet wheel and the spool. One end of the torsion bar is coupled to the spool and the other end is coupled to the ratchet wheel. When a force drawing the webbing exceeds a certain limit, the torsion bar is subjected to twist deformation between the spool around which the webbing is wound and the ratchet wheel which is in a locked condition by the meshing with the pawl, so that the spool rotates by a predetermined amount with respect to the ratchet wheel, and the impact load acting on the webbing is absorbed (for example, see Japanese Patent Publication (Kokai) No. HEI10-250529).
In the above-mentioned seat belt retractor provided with the energy absorption mechanism mainly including the torsion bar, however, in addition to the ratchet wheel, an inertia sensing device (a locking arm, a locking arm base, or the like) which rotates in synchronization with the torsion bar and which is synchronized so that the ratchet wheel and the pawl precisely mesh with each other is coupled to the torsion bar.
In a seat belt retractor in which an energy absorption mechanism is not added, when a spindle of a spool corresponding to the torsion bar and a ratchet wheel of an emergency locking mechanism are integrally formed, precise synchronization can be relatively easily realized by a combination in which the angular phase of the spindle with respect to other members is constant. In the torsion bar of the energy absorption mechanism, soft steel which is easily subjected to twist deformation is used. On the other hand, in the ratchet wheel of the emergency locking mechanism, hard steel is used because the ratchet wheel is required to withstand an extremely large load at the time of lock due to meshing with the pawl. For this reason, they cannot be integrally formed. Accordingly, the torsion bar and the ratchet wheel are formed as individual members and the following structure is adopted. As disclosed in above-described Japanese Patent Publication (Kokai) No. HEI10-250592, for example, a coupling portion of a hexagonal shape is formed at one end of the torsion bar, and a hexagonal insertion hole for fitting the coupling portion of the torsion bar is formed in the ratchet wheel. The coupling portion of the torsion bar is fitted into the insertion hole, thereby coupling them with each other.
However, in order to enable the coupling portion of the torsion bar to be fitted into the inserting hole of the ratchet wheel, a gap of a certain size or more is naturally required between them. For this reason, at the time of the coupling of these members, there inevitably occurs a little combination error in a circumference direction. As a result, as the number of incorporated components is larger, it becomes more difficult to precisely maintain the synchronization of the components in accordance with the design. This results in a problem that the emergency locking mechanism is out of synchronization, so that the winding of the webbing or the drawing disabled condition (lock-up phenomenon) is caused.
In the above-identified Japanese Patent Publication (Kokai) No. HEI10-250592, a technique for applying a previous twist to the torsion bar to variously change an energy absorption load by using only one kind of torsion bar is disclosed. The publication also discloses that, for the purpose of identifying the previous twist angle, a cutout or a projection is disposed in one position in a circumference direction on surfaces of coupling portions at both ends of the torsion bar made of soft steel to the spool and the ratchet wheel. The publication describes that, in the case where the projection is disposed, at the time of insertion into the insertion hole of the ratchet wheel, the projection is broken, so that rattling between the insertion hole and the coupling portion of the torsion bar can be eliminated.
The projection formed in one position in the circumference direction on the side of the torsion bar made of soft steel has an effect that, at the insertion into the insertion hole, the projection is appropriately deformed, so as to eliminate a gap with the insertion hole, and rattling therebetween is effectively eliminated in a condition in which any force is not applied. When a twisting moment acts on the torsion bar, however, the projection is easily deformed further because the projection is disposed on the side of the torsion bar made of soft material, and a relative displacement is easily caused as a result of that the projection is scraped by the coupling portion to the ratchet wheel. When such a twisting moment repetitively acts, rattling eventually occurs between them, and there arises a possibility that the synchronization of the emergency locking mechanism cannot be attained. Even if such a projection is disposed on an outer circumference of the torsion bar, it is impossible to eliminate a combination error in an angular phase between the torsion bar and the ratchet wheel.
The invention has been conducted in view of the above-mentioned circumstances. It is an object of the invention to provide a seat belt retractor in which a torsion bar of an energy absorption mechanism and a ratchet wheel of an emergency locking mechanism can be easily combined with good reproducibility and in a constant angular phase without requiring any special precise working, which stably and surely operates without causing the emergency locking mechanism to be out of synchronization, and in which an energy can be effectively absorbed without accompanying any time delay.
Specifically, in order to attain the above-mentioned object, the seat belt retractor of the invention is a seat belt retractor in which the seat belt retractor comprises: a spool for winding a webbing; and
an emergency locking mechanism including: a ratchet wheel which rotates together with the spool; and a pawl which meshes with the ratchet wheel in response to emergency detection by inertia sensing means, thereby setting the spool into a locked condition via the ratchet wheel, and
a torsion bar is disposed between the spool and the ratchet wheel, one end of the torsion bar being coupled to the spool, another end of the torsion bar being coupled to the ratchet wheel, the torsion bar being subjected to twist deformation to absorb an impact when a force in a drawing direction acts on the webbing in an operating condition of the emergency locking mechanism, and characterized in that a coupling portion of the torsion bar with respect to the ratchet wheel is formed into a polygonal shape, a polygonal insertion hole into which the polygonal coupling portion is to be fitted is formed in the ratchet, and a rib-like projection is formed on an inner face of the polygonal insertion hole in an axial direction of the torsion bar, the rib-like projection biasing, when the webbing is drawn, the torsion bar in the insertion hole in a direction along which the torsion bar rotates, to cause respective faces to be in press contact with each other in the direction.
In the invention, as the polygonal shape of the coupling portion of the torsion bar with respect to the ratchet wheel, a polygonal shape such as a hexagon or an octagon, or another polygonal shape in which concaves and convexes are formed at a predetermined interval in a circumference direction can be adopted. As a more specific shape in such a case, for example, a star shape, a spline tooth shape, a serration tooth shape, and the like can be employed.
In the invention, it is preferred to adopt a configuration in which the rib-like projection is formed in at least three positions on the inner face of the polygonal insertion hole at predetermined intervals in the circumference direction.
The rib-like projection in the invention is desirably formed from a position which is distant away from an open end of the polygonal insertion hole on a torsion bar insertion side by a predetermined distance, to an inner side.
In the invention, each of the coupling portion of the torsion bar with respect to the ratchet wheel, and the insertion hole of the ratchet wheel into which the coupling portion is to be fitted has a polygonal shape, and a rib for biasing the torsion bar in a predetermined direction in the insertion hole so that the respective faces closely come into contact with each other in the predetermined direction is formed in the insertion hole of the ratchet wheel, thereby enabling the torsion bar and the ratchet wheel to, when the coupling portion of the torsion bar is fitted into the insertion hole of the ratchet wheel, be combined so as to always attain a constant angular phase between torsion bar and the ratchet wheel. The rib-like projection is disposed on the side of the insertion hole of the ratchet wheel of a harder material, so that the rib-like projection is not broken at the insertion of the torsion bar, and the projection is engaged so as to scrape the side of the coupling portion of the torsion bar. Thus, the faces on the opposite sides strongly come in press contact with each other, so that the torsion bar and the ratchet wheel are always combined in a constant angular phase.
The direction of biasing of the torsion bar in the insertion hole is set to the direction in which the torsion bar rotates when the webbing is drawn out. Therefore, a face of the coupling portion of the torsion bar is initially in press contact with a face of the insertion hole of the ratchet wheel in the rotation direction. When an impact load acts on the webbing in a crash of a vehicle or the like and a torque in a direction of drawing out the webbing acts on the torsion bar via the spool, consequently, a relative rotation between the torsion bar and the ratchet wheel is not caused. Thus, twist deformation is immediately caused without producing any time delay, so that an energy can be effectively absorbed.
According to the invention, the coupling portion of the torsion bar and the insertion hole of the ratchet wheel have a polygonal shape in which concaves and convexes are formed at a predetermined interval in the circumference direction. When the coupling portion is biased in the insertion hole in the above-mentioned direction, therefore, the concaves and convexes of the coupling portion and the insertion hole are in press contact with each other in a mutual face abutting manner. Accordingly, the effect for preventing the relative rotation of the torsion bar and the ratchet wheel from occurring can be more surely attained.
In addition, when the configuration of the invention in which the rib-like projection formed in the insertion hole of the ratchet wheel is formed in at least three positions at predetermined intervals in the circumference direction is employed, the torsion bar is not partially biased in the insertion hole, but is always precisely biased in the above-mentioned direction, so that the respective faces can be surely and closely in contact with each other in the direction.
According to the invention, the above-mentioned rib-like projection is not formed in the vicinity of the open end on the torsion bar inserting side of the insertion hole of the ratchet wheel, but formed in a position distant away from the open end by a predetermined distance. With this configuration, when the coupling portion of the torsion bar is being inserted, it is possible to insert the coupling portion of the torsion bar into the insertion hole in a condition where they are easily and surely positioned, because a certain degree of gap exists between the insertion hole and the coupling portion of the torsion bar in an initial stage of the insertion. Thus, it is advantageous that the combining work can be facilitated.